package com.example.dragon.untis;



/**
 * Created by 徐国峻 on 2016/11/7.
 */

public class Zuobiao {


    /**
     * Returns distance on the unit sphere; the arguments are in radians.
     */
    private static double distanceRadians(double lat1, double lng1, double lat2, double lng2) {
        return arcHav(havDistance(lat1, lat2, lng1 - lng2));
    }

    /**
     * Computes inverse haversine. Has good numerical stability around 0.
     * arcHav(x) == acos(1 - 2 * x) == 2 * asin(sqrt(x)).
     * The argument must be in [0, 1], and the result is positive.
     */
    static double arcHav(double x) {
        return 2 * Math.asin(Math.sqrt(x));
    }

    /**
     * Returns hav() of distance from (lat1, lng1) to (lat2, lng2) on the unit sphere.
     */
    static double havDistance(double lat1, double lat2, double dLng) {
        return hav(lat1 - lat2) + hav(dLng) * Math.cos(lat1) * Math.cos(lat2);
    }

    /**
     * Returns haversine(angle-in-radians).
     * hav(x) == (1 - cos(x)) / 2 == sin(x / 2)^2.
     */
    static double hav(double x) {
        double sinHalf = Math.sin(x * 0.5);
        return sinHalf * sinHalf;
    }

    private static final double EARTH_RADIUS = 6378137.0;
    public static void main(String[] args) {
        double lo1 = 108.90, la1 = 34.1;// 第一个经纬度
        double lo2 = 115.4648060, la2 = 38.8738910;// 第二个经纬度
        System.out.println("经纬度结果:" + getDistance(lo1, la1, lo2, la2));
        System.out.println("经纬度结果:" + getDistance(0, 0, 0, 0));
    }
    // 返回单位是米
    public static double getDistance(double longitude1, double latitude1,
                                     double longitude2, double latitude2) {
        double Lat1 = rad(latitude1);
        double Lat2 = rad(latitude2);
        double a = Lat1 - Lat2;
        double b = rad(longitude1) - rad(longitude2);
        double s = 2 * Math.asin(Math.sqrt(Math.pow(Math.sin(a / 2), 2)
                + Math.cos(Lat1) * Math.cos(Lat2)
                * Math.pow(Math.sin(b / 2), 2)));
        s = s * EARTH_RADIUS;
        s = Math.round(s * 10000) / 10000;
        s = s/2000;
        return s;
    }
    private static double rad(double d) {
        return d * Math.PI / 180.0;
    }

}
